"It is really exciting that they were able to extract phytoliths from the dental calculus [plaque]," says Leslie Aiello, president of the Wenner-Gren Foundation for Anthropological Research in New York. "This is important information about detailed plant consumption in the hominins – something that has been invisible to us."

Hard evidence

Greater dietary surprises were in store for Berger and his colleagues though. The team looked at sediment samples and fossilised animal faeces – coprolites – to get an idea of what the environment in which A. sediba lived was like. They found remnants of savannah grasses in the sediment, and pollen and woody fragments in the coprolites suggested that there might have been some woodlands in the vicinity.

The team then looked at the carbon isotopes in A. sediba teeth to see what types of plants they ate. A "C4" signature is typical of savannah plants like grasses and the grains they carry. These plants fix carbon in a four-carbon molecule. "C3" indicates fruits and leaves foraged from a more forested environment.

The team expected a C4 signature – it’s what most hominins have and fits the evidence that A. sediba lived in an open savannah. They found the exact opposite. The results are fascinating, says Aiello. "The most important thing is that the diet of A. sediba was different from the diet of other early hominins."

Why A. sediba had such an unusual diet is still a mystery.

Henry suggests that A. sediba may have lived in small woodlands that lined bodies of water in the savannah. Its lifestyle may have been similar to savannah chimps, which travel long distances to forage the limited woodlands available to them.

"They may have been trying new things. We’re getting an idea of what comes later when modern humans became so flexible that they could exploit almost any environment," she says.

To Berger one thing is clear: A. sediba was a picky eater – and picky eaters are clever. "They had to be smart enough to select specific foods from their environment," he says.